1. Field of the Invention
The present invention relates to an ion implanter and a method of tuning an ion beam.
2. Description of the Related Art
An ion implanter including a radio frequency linear accelerator is known. Such an ion implanter is used for high energy ion implantation in a normal case. An ion beam accelerated or decelerated by the radio frequency linear accelerator has a certain energy width. That is, the ion beam exiting from the radio frequency linear accelerator contains not only ions having desired energy but also ions having higher (or lower) energy than it. Thus, an energy analysis magnet and an energy analysis slit can be provided at the downstream of the radio frequency linear accelerator. The energy analysis magnet can convert energy deviation among the accelerated or decelerated ions into ion trajectory deviation. Since the energy analysis slit is arranged on a trajectory of ions having specified energy, the ions having the energy pass through the energy analysis slit and are guided to a workpiece.
Ideally, the energy analysis slit allows only ions having desired energy to pass therethrough and blocks ions having different energy from it. However, in reality, the energy analysis slit has a certain small slit width. For this reason, the energy analysis slit allows not only the ions having desired energy but also ions having slightly higher energy (or slightly lower energy) than the desired energy to pass therethrough.
The narrower the slit width of the energy analysis slit is, the more the resolution is improved, which contributes to improvement of implantation energy precision to a workpiece. On the other hand, since the amount of the ion beam passing through the slit is reduced, productivity of the ion implanter is lowered. In this manner, in an existing high energy ion implanter, the energy precision and the productivity are in a trade-off relationship regarding design of the energy analysis slit.